Sphyrnidae

Elasmobranch, Its Implications For Global, Parasitology, Diversity And, Naylor, G. J. P., Sc, Caira, J. N., Ct, Jensen, K., Ks, Rosana, K. A. M., Fl, White, W. T., Csiro, Tas, Last, P. R., Csiro & Tas, 2012, A Dna Sequence-Based Approach To The Identification Of Shark And Ray Species And Its Implications For Global Elasmobranch Diversity And Parasitology, Bulletin of the American Museum of Natural History 2012 (367), pp. 1-262 : 31-33

Sphyrnidae (hammerhead sharks)

Our analysis includes representation of seven of the eight described species of hammerhead sharks. However, we believe it also includes specimens of three undescribed species of hammerheads. To allow comparison of genetic variation across species, the haplotype maps presented for hammerheads ( fig. 87A, B) include all 10 of these species. The implications of these maps for the three species complexes ( S. lewini , S. zygaena , and S. tiburo ) are each treated separately below. However, from the standpoint of the family in general, it is interesting to note that the haplotype map colored by geography ( fig. 87B) illustrates that hammerheads are among the most widely distributed species of elasmobranchs. For example, the same haplotype of S. lewini 1 is found in animals from the western Indian Ocean, India, and South China Sea. Similarly, the same haplotype of S. zygaena is found in animals from Taiwan, Borneo, and northern Australia. Little variation is seen in the haplotypes of individuals of S. lewini 2 that occur in Borneo, Taiwan, and the Gulf of California. Little variation is seen in the haplotypes of individuals of S. zygaena from the Gulf of Mexico, western North Atlantic, Senegal, Japan, Taiwan, Vietnam, and the Gulf of California. Nevertheless, it seems there is a great deal of sympatry. For example, the western Atlantic (including the Gulf of Mexico and Trinidad) is home to six species of hammerheads ( S. lewini 2, S. mokarran 1, S. tiburo , S. cf. tiburo , S. tudes , and S. zygaena ).

Sphyrna lewini (scalloped hammerhead) complex

( fig. 19)

Our analysis included a total of 45 specimens initially identified as the scalloped hammerhead S. lewini . These came from the western North Atlantic (11 specimens), the Gulf of Mexico (6 specimens), Senegal (4 specimens), Madagascar (3 specimens), India (5 specimens), Borneo (10 specimens), Gulf of California (2 specimens), and Taiwan (4 specimens). Given that the type locality of this species is southern Australia, the unavailability of specimens from Australia was unfortunate. Our analysis yielded considerable structure among S. lewini . First, the analysis yielded two strongly divergent clusters, each with some substructure. However, at this time we have recognized only the two main clusters. The 32 specimens comprising the first cluster, from the western Atlantic, Gulf of Mexico, Senegal, Madagascar, India, and Malaysian Borneo, have been designated Sphyrna lewini 1, and the 13 specimens comprising the second cluster, from the Gulf of California, Borneo, and Taiwan, have been designated Sphyrna lewini 2; one specimen from the latter cluster is vouchered (GN4187 5 CAS 229024). Within the S. lewini 1 cluster, the specimens from the Gulf of Mexico and the western North Atlantic comprised a weak subcluster; the specimens from Senegal comprised a second weakly supported subcluster, and the specimens from India, Madagascar, and those from Malaysian Borneo comprised a third weakly supported subcluster. In addition, the specimens from Madagascar and India and three of the specimens from Borneo comprised a subcluster. Within the Sphyrna lewini 2 cluster, there was evidence of a subcluster consisting of a specimen from Taiwan and one from Malaysian Borneo. The range in pairwise differences among all 45 specimens of S. lewini was 0–78. The range in pairwise differences within the S. lewini 1 cluster was 0–12, with an average of 4.4. The range within the S. lewini 2 cluster was 0–21, with an average of 7.2. The average of the pairwise differences between specimens of S. lewini 1 and S. lewini 2 was 64.2. These results suggest that undescribed diversity exists among scalloped hammerheads, which may include sympatric species. This result is consistent with those of a number of previous authors who also reported genetic diversity within S. lewini (e.g., Abercrombie et al., 2005; Duncan et al., 2006; Quattro et al., 2006; Zemlak et al., 2009).

The haplotype map colored by phenotype ( fig. 87A) supports recognition of S. lewini 1 and S. lewini 2 as they exhibit distinct, but relatively tight clusters of haplotypes. The haplotype map colored by geography ( fig. 87B) illustrates the relatively broad distributions of both of these clusters of haplotypes ( fig. 87B).

Sphyrna tiburo (bonnethead shark) complex ( fig. 19)

All 14 specimens originally identified as S. tiburo were collected from the Gulf of Mexico (12 specimens) and Trinidad (2 specimens). As a consequence, our sample represents only a portion of the distribution of this species along the western Atlantic seaboard, and we have no representation of the eastern Pacific portions of the distribution of this species. The analysis yielded some geographic structure in that the specimens from the Gulf of Mexico clustered together as did those from Trinidad. The range in pairwise differences among bonnetheads overall was 0–28. The range in pairwise differences within the Gulf of Mexico cluster was 0–3, with an average of 0.6, and the two specimens from Trinidad differed by 4. The average of the pairwise differences between the two clusters was 25.3. In recognition of the fact that the type locality of S. tiburo is America, we have given the Trinidad specimens the designation Sphyrna cf. tiburo . However, the type locality of S. tiburo is imprecise so the nomenclature of this group needs to be examined more thoroughly.

The haplotype map colored by phenotype ( fig. 87A) supports the distinction between S. tiburo and S. cf. tiburo .

Sphyrna tudes (smalleye hammerhead) ( fig. 19)

Our analysis included four specimens, all collected from Trinidad. Thus, our sample comes from a relatively northerly locality within the distribution of this species, which extends along the east coast of South American to Argentina. The analysis yielded a single cluster. The range in pairwise differences within the cluster was 0–6, with an average of 3.

Sphyrna corona (mallethead shark) ( fig. 19)

The six specimens included in the analysis all came from the western coast of Panama. Thus, they represent the central region of the distribution of this species, which extends along the western seaboard of the Americas from the Gulf of California to Peru. The analysis yielded a single cluster. The range in pairwise differences within this cluster was 0–7, and the average was 3.3.

Sphyrna mokarran (great hammerhead) complex

( fig. 19)

In total, 22 specimens were included. These were collected from the Gulf of Mexico (9 specimens), the western North Atlantic coast from Massachusetts to Florida (7 specimens), Malaysian Borneo (1 specimen; GN3471 5 IPPS BO254 ), and northern Australia (5 specimens). Given that this species has been reported to occur in a global band ( Last and Stevens, 2009), on continental shelves throughout the tropics and subtropics, our sample largely underrepresents the distribution of this species, and does not include the type locality (Red Sea). Nonetheless, the analysis yielded two distinct clusters: one comprised of the specimens collected from the Atlantic, which we refer to as Sphyrna mokarran 1, and a second consisting of specimens from Australia and Borneo, which we refer to as Sphyrna mokarran 2. The range in pairwise differences among S. mokarran specimens overall was 0–16. The range in pairwise differences among specimens of S. mokarran 1 was 0–3 (with an average of 0.5) and the range in pairwise differences among specimens of S. mokarran 2 was 0–4 (with an average of 1.9). However, the average of the pairwise differences between these two clusters was 14.1 .

Although they are not among the most divergent of the hammerhead species complexes treated here, there is no haplotype overlap between specimens of S. mokarran 1 and S. mokarran 2 ( fig. 87A), which supports recognition of these as distinct allopatric species ( fig. 87B).

Sphyrna zygaena (smooth hammerhead) ( fig. 19)

The 16 specimens of this species were collected from the Gulf of California (4 specimens), western North Atlantic (6 specimens), Senegal (1 specimen), Vietnam (1 specimen), Taiwan (3 specimens), and Japan (1 specimen), and thus represent at least the longitudinal (if not the latitudinal) distribution of this species. The analysis yielded essentially a single cluster, with a range in pairwise differences among specimens of 0–8, with an average of 2.5. One of the specimens from the Gulf of California was vouchered (GN1097 5 IBUNAM PE9519).

Eusphyra blochii (winghead shark) ( fig. 19)

All nine of our specimens of this species were all collected from Fog Bay, in the Timor Sea of northern Australia and thus represent only a small portion of the distribution of this species, which includes much of the coastal regions of the Indo-West Pacific. The analysis yielded a single cluster of specimens with a very low range in pairwise differences among specimens (i.e., 0–2); one of these samples was vouchered (GN1256 5 NTM S.14689-004).